1. Field of the Invention
The present invention relates to a device for reliably feeding sheets to an automatic photographic processor or the like, one by one, from a stack of sheets.
2. Description of the Related Art
A sheet feeding device has been used to deliver sheets such as unexposed photographic light-sensitive mediums, one by one, from either a supply magazine or a sheet placement table in which the sheets have been stored in a stacked state. The sheets are delivered to an exposure station and after the sheets have been exposed, are fed one by one to a developing machine.
The sheet feeding device is so constructed that a plurality of suction cups or pads (sheet separating means) are positioned to face a sheet stack. The suction pads are pressed against an uppermost sheet of the stacked sheets to hold and remove the uppermost sheet under a suction generated by a vacuum generator.
Different sized sheets such as photographic films are employed for various uses. Such different sized sheets are fed one by one by use of a single sheet feeding device. In this sheet feeding device, one or more suction pads are disposed to face one end of an edge of the uppermost sheet of the sheets so as to meet the smallest sized sheet of the different sized sheets to avoid air leakage that would result when the smallest sized sheet is attracted. Therefore, when a sheet of particularly a large size is employed, the opposite end of the sheet with regard to the suction pads is spaced a long distance away from the suction pads, which results in the sheet hanging due to its own weight or stiffness. Thus, the opposite end of the sheet is brought into contact with an engaging member which holds the stacked sheets on a sheet placement table, thereby creating a failure during sheet feeding or damage to the sheets.
In order to avoid the hanging of the opposite end of the sheet with regard to the suction pads when the uppermost sheet is attracted under suction by the suction pads, the following approaches have heretofore been made. Specifically, a sheet placement table or portion is formed in such a shape that the portion can upwardly tilt the opposite end of the sheet which may hang down. Alternatively, there is located at least one auxiliary suction pad opposing the opposite end of the sheet which may hang down. When sheets of, for example, large size are fed one by one, the auxiliary suction pad is driven to hold the opposite end of the sheet under suction.
In the conventional sheet feeding device, however, a process for loading a plurality of sheets in the sheet placement portion having shape referred to the above is greatly cumbersome, thereby causing the problem that the sheet feeding process as a whole cannot efficiently be carried out.
When the auxiliary suction pad referred to above is provided, the pad must be activated only when the sheets of large size are fed one by one, thereby causing the problem that control of the auxiliary suction pad is complicated and hence its operation efficiency becomes inferior.
In addition to the above problems, there is often a situation in which the stacked sheets adhere firmly to one another. It is therefore necessary to reliably separate only the uppermost sheet from the adjacent lower sheets by suction cups or pads so as to remove the uppermost sheet from the sheet placement portion. To this end, there have heretofore been proposed various approaches. In general, the uppermost sheet attracted by the suction pads is moved along complicated loci or paths to have the sheet turned or swung, thereby preventing a plurality of sheets from being fed simultaneously.
In the conventional sheet feeding device referred to above, however, an extremely complex mechanism is required for turning or swinging the uppermost sheet. Thus, the entire construction of the sheet feeding device becomes complex and the manufacturing cost is rendered high.
There is also a case in which when the lower sheets underneath the uppermost sheet are successfully separated from the uppermost sheet attracted performing the suction pads by sheet turning or swinging action. In this case, however, the lower sheets are held in the sheet successfully removed at times cannot reliably be returned into a sheet placement portion. Therefore, a pressing bar must normally be used, so that the sheet feeding process cannot efficiently be carried out.